Good-quality images are key for interpreting OCT angiography (OCT-A) images correctly, and as the sensitivity of instruments increases, they run the risk of error from even marginal abnormalities of the ocular media. Image quality may be affected by a number of factors, including scan pattern, retinal disease, signal strength, axial length and the patient’s ability to hold their eye open for a period of time. The latter, researchers note, may “induce instability of the tear film,” affecting the quality of the scan.

A recent study found that OCT-A’s repeatability and signal strength may indeed be influenced by a patient’s dry eye status. Researchers hypothesized that an unstable tear film could affect the quality of OCT-A and compared the test’s repeatability based on tear break-up time (TBUT).

They performed 3x3mm OCT-A twice in 112 eyes, which were divided into three groups according to their TBUT (Group 1: five seconds or less; Group 2: six to 10 seconds; and Group 3: 11 seconds or more).

The researchers found a significant difference among OCT-A signal strengths in the three groups (9.1, 9.5 and 9.5in groups 1, 2 and 3, respectively). They also found that the intraclass correlation coefficient values of vessel density increased in order from Group 1 to Group 3. Coefficient of variation and test-retest standard deviation values decreased significantly in order from Group 1 to Group 3.

"The tear film is the first entry point of light,” the researchers wrote in their paper. “When being examined by OCT-A, patients keep their eyes open for a certain period, which may induce instability of the tear film. Several studies had reported that tear break-up reduced the optical quality.”

They believe that tear film instability leads to higher corneal aberrations that attenuate and defocus the OCT-A beam. “We found TBUT was the significant factor influencing OCT-A repeatability in multivariate analyses,” they wrote.

The researchers concluded that OCT-A’s repeatability tended to decrease with a shorter TBUT. “When the TBUT is less than five seconds, care must be taken to interpret the OCT-A results correctly,” they noted.